The present invention relates to an automatic modulation type discrimination apparatus, particularly an automatic modulation type discrimination apparatus and automatic modulation type discrimination method for automatically discriminating a modulation type of a reception signal having unknown communication elements, and to a magnetic recording medium in which a program for operating the apparatus and implementing the method has been recorded.
Hitherto, as to this kind of apparatus for discriminating a modulation type of reception signal, there is, for example, a reception signal discrimination circuit disclosed in U.S. Pat. No. 5,600,673. This recreation signal discrimination circuit is applied to a radio communication system using the same frequency band in a connection communication between isolated islands and an urgent communication in an emergency, and used in order to discriminate an urgent communication signal accurately and at high speed.
The reception signal discrimination circuit mentioned above is explained by referring to FIG. 1. In FIG. 1, the reception signal discrimination circuit includes a clock extraction circuit 111 for extracting a data clock from demodulated reception data. A phase difference measurement circuit 112 measures a phase difference between the data clock extracted by the clock extraction circuit 111 and the demodulated reception data. A deviation calculation circuit 113 calculates a deviation between the phase deviation measured by the phase difference measurement circuit 112 and a reference value for deviation predetermined on the basis of modulation type. A squaring calculation circuit 114 squares the deviation calculated by the deviation calculation circuit 113. An average value calculation circuit 115 calculates an average value of plural numbers of continuous predetermined squared value outputs calculated by the squaring calculation circuit 114. A comparison circuit 116 compares as to which is lager the average value calculated by the average value calculation circuit 115 or a predetermined reference value for determination, and outputs a discrimination signal on the basis of the comparison result.
Next, an operation of the reception signal discrimination circuit is explained. An object of the reception signal discrimination circuit is to discriminate whether or not reception data of a desired modulation type are inputted. Incidentally, a demodulator of the modulation type becoming a discrimination object is placed in a front stage of an input portion of reception data, and the reception signal discrimination circuit performs the discrimination from a clock number for phase difference measurement included in one bit data interval of demodulated reception data. This utilizes a characteristic that, in case where the reception data are reception data of the desired modulation type, a clock number becomes constant but, in case where it is reception data of another modulation type, its value becomes an unstable value.
Accordingly, with this reception signal discrimination circuit, first in case where the reception data other than the desired modulation type are received, it is impossible to specify that modulation type. Further, on discriminating, since it is a premise that the discrimination is performed using the demodulated reception data, it is necessary that communication elements required for demodulating the reception signal is previously known.
Concretely, the reception signal is first demodulated by a demodulator in which the communication elements necessary for the demodulation have been set. Thereafter, the demodulated reception data are inputted to the circuit shown in FIG. 1, and the data clock is extracted by the clock extraction circuit 111. Next, the reception data and the extracted data clock are inputted to the phase difference measurement circuit 112. The phase difference measurement circuit 112 has a phase difference measurement clock of prescribed frequency, which is fixed therein. The phase difference measurement circuit 112 computes a clock number for the phase difference measurement between from a change point of the reception data to a leading edge of a next data clock.
In FIG. 2A to FIG. 2C, there are shown waveform diagrams in case where the reception data of the desired modulation type are inputted. FIG. 3A to FIG. 3C show waveform diagrams in case where the reception data other than the desired modulation type are inputted. FIG. 2A, FIG. 3A show the waveforms of the demodulated reception data, and FIG. 2B, FIG. 3B show the waveforms of the data clock. FIG. 2C, FIG. 3C show waveforms of measured data clock of the phase difference measurement clock.
As apparent from FIG. 2A to FIG. 2C, in case where the reception data of the desired modulation type are inputted as the reception signal, the measured clock number becomes a constant value. However, as shown in FIG. 3A to FIG. 3C, in case where the reception data not modulated by the desired modulation type are inputted, the change point of the reception data becomes random, and also the measured number of the phase difference measurement clock becomes random. From the results mentioned above, it is made possible to determine whether or not the reception data are the desired modulation type.
Incidentally, the deviation calculation circuit 113, the squaring calculation circuit 114 and the average value calculation circuit 115 are calculation circuits used for the purpose of increasing an accuracy when performing the discrimination processing, by utilizing the aforesaid characteristic. The comparison circuit 116 determines, from the inputted calculation result, whether or not the reception signal is a signal by the desired modulation type.
As mentioned above, in the prior art, it is an object to discriminate whether or not the reception data of the desired modulation type are received. Further, for the discrimination processing, the demodulated reception data are used and, in order to obtain this demodulated reception data, there are beforehand required the communication elements necessary for demodulation and the demodulator therefor.
Besides, as to a circuit for discriminating whether or not the reception signal is the desired modulation type, there is a discrimination circuit disclosed in the aforesaid U.S. Pat. No. 5,600,673. This discrimination circuit is shown in FIG. 4. In FIG. 4, this discrimination circuit extracts the clock data from the demodulated reception data by a PPL (Phased Lock Loop) circuit 119, the reception data are decoded in a decoding circuit 117 by the extracted data clock. Subsequently, a synchronous code is detected by a synchronous code detection circuit 118 from the extracted data clock and the decoded data. By using the detected synchronous code, it is discriminated whether or not the reception data are the desired modulation type.
That is, in this discrimination circuit, the discrimination is performed paying attention to the synchronous code after the decoding. Further, the discrimination is only a discrimination as to whether or not it is the desired modulation type. Furthermore, on discriminating, the communication elements (including the synchronous code) for obtaining the synchronous code must be previously known and the demodulator for demodulation is required.
As apparent from the explanation mentioned above, in the conventional modulation type discrimination method, there are problems mentioned below.
A first problem exists in the fact that, with the conventional discrimination circuit mentioned above, it is only possible to discriminate whether or not the reception data are a signal of the desired modulator type. This means that the received reception data of another modulation type do not become an object of the modulation discrimination. Therefore, in case where plural kinds of modulation types are made the discrimination object, an apparatus becomes large-sized, so that it becomes a problem also in terms of a flexibility of the apparatus.
A second problem is the fact that, with the conventional discrimination circuit, the communication elements must be previously known for the discrimination. This is because the data used in the discrimination are the reception data after the demodulation and the synchronous code after the decoding. In order to obtain these data and code, there are beforehand required the communication elements of the modulator type which is the discrimination object and the demodulator in which the communication elements are set. Here, in case where these are not previously known, accurate data used in the discrimination are not obtained, so that it is difficult to perform the discrimination processing.
A third problem is the fact that, in case where the communication elements of the signal which is the discrimination object changes, it is impossible to deal with the change. This is because, with the conventional discrimination circuit, it is a premise that a modulation type is discriminated by the reception data after having been demodulated using the known communication elements. This is also because it does not have a communication wave elements extraction circuit capable of dealing with a change in the communication elements and means for analyzing that change.
A fourth problem is the fact that, with the conventional discrimination circuit, a long time is required for the decoding and the detection of the synchronous code, so that it is impossible to perform the discrimination at high speed. This is because, in the example of FIG. 4, notwithstanding the fact that the synchronous data, i.e., usually data and the like, exist at the beginning of the reception data, it must pass through a detection of the synchronous code existing thereafter.
A fifth problem is the fact that, in case where plural kinds of conventional discrimination circuits are combined and plural kinds of modulation types are made an object of the discrimination, a circuit scale becomes large and complex, so that a necessary calculation amount is greatly increased. This is because, in order that the plural kinds of modulation types are made an object of the discrimination, it is necessary to adopt a constitution in which such a constitution as shown in FIG. 1 is arranged in parallel in plural number.